     (init-state [_]
       {:header-logo-visible false
        :header-cta-visible false
+       :header-bkg-visible false
        :scroll-ch (chan (sliding-buffer 1))})
     om/IRenderState
     (render-state [_ state]

        (html [:div.home.page
               [:nav.home-nav {:class (concat
                                       (when (:header-logo-visible state) ["logo-visible"])
                                       (when (:header-cta-visible state) ["cta-visible"]))}
                [:a.promo "What is Continuous Integration?"]
                [:a.login "Log In"]
                (om/build drawings/logo-circleci app)
                [:a.action "Sign Up Free"]]
               [:section.home-prolog
                [:a.home-action {:role "button"
                                 :ref "cta"}
                 "Sign Up Free"]

(defn mount-header-logo-scroll [owner]
  (let [logo (om/get-node owner "center-logo")
        cta (om/get-node owner "cta")
        nav-bkg (om/get-node owner "nav-bkg")
        scroll-callback #(do
                           (om/set-state! owner [:header-logo-visible] (neg? (.-bottom (.getBoundingClientRect logo))))
                           (om/set-state! owner [:header-cta-visible] (neg? (.-bottom (.getBoundingClientRect cta))))
                           (om/set-state! owner [:header-bkg-visible] (< (.-bottom (.getBoundingClientRect nav-bkg)) 70)))]
    (om/set-state! owner [:browser-resize-key]
                   (goog.events/listen
                    (sel1 (om/get-shared owner [:target]) ".app-main")
